How should scientists and journalists report risk? The way in which a statistic is presented can entirely change how alarming it sounds. And too often, both newspapers and scientific journals choose the most alarming, but least informative, way.
For instance, according to a study published in the Ěýthis month, if you father children in your fifties, your children are more likely to suffer various health issues, including seizures. Specifically, if you are aged 45 to 54 when you become a father, your children are 18Ěýper cent more likely to suffer seizures than if you are 25-34.
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Since many people these daysĚýhave children in midlife, that is an alarming statistic. But it is misleadingly so. It is presented as what is known as “relative risk”: how likely one group is to have seizures compared to the other. But it doesn’t tell you how likely your child actually is to have seizures.
That figure is known as “absolute risk”, and it is both more revealing and more reassuring. Your child’s absolute risk of suffering seizures if you have a child when you are 30 is 0.024Ěýper cent: that is, 24 out of every 100,000. If you have a child at 50, it is 0.028Ěýper cent. , a statistician at the University of Oxford, says: “An 18Ěýper cent increase sounds shocking, but in reality, it will affect four people in every 100,000.”
It’s all relative
The difference is vital. But too often, when scientific stories are reported in the news, we read about relative, rather than absolute, risk. żěè¶ĚĘÓƵĚýhas not been immune to the tendency, and the “older fathers” story is not the only one in recent weeks: the BBC Radio 4 Today programme discussed a conference paper finding a “100Ěýper cent increase” in breast cancer risk among women who prefer to sleep and stay up late, compared to those who get up and go to bed early. But, as the much better on the BBC website made clear, the absolute risk in a given eight-year window was 2 in 100 for “night owls”, compared to 1 in 100 for “larks”.
“Relative risk is fine for scientific inference,” says , professor of the public understanding of risk at the University of Cambridge. So if you’re interested, from a purely scientific point of view, in whether two things are associated – whether your risk of cancer is linked to how much meat you eat – then it’s helpful. But if you want to help people make decisions about their life, “it’s useless,” he says. “It’s totally the wrong measure. You cannot decide what’s an appropriate action without absolute risk.”
This is not just an issue for the media: journals and scientists often fail to report absolute risk prominently. The BMJ study above reported all its findings in relative risk, hiding the absolute risk away in a table, despite their saying “Whenever possible, state absolute rather than relative risks”. And in August, the Lancet published a on the health impacts of drinking which concluded that there was “no safe level”. But it, too, gave relative risks, also against its own .
Insist on absolute
The Lancet press office, admirably, managed to get the absolute risks from the authors for its . But if scientists don’t make it easy to find, then journalists, who are often not especially numerate, “can only report the relative risk”, says Rogers.
If the study or story has any recommendations about individual action or policy, then scientists and journalists should both insist on reporting it in absolute risk, says Spiegelhalter. “It’s so irritating that they don’t. We know from both experience and research that absolute risk, and especially the expected number of people – what does it mean per 1,000 people or per 100 – is such a clear way of communicating.”
He added: “One must suspect that the reason it’s sometimes not done is because when it’s not put in those terms, the effects don’t seem very important.”
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